Holographic optical element with castellated aperture

Abstract

In an optical positioning system, a holographic optical element having a plurality of rectangular apertures has predetermined ones of its aperture edges castellated or notched in order to null out undesired light energy in target areas. The apertures may be fitted with diffraction grating patterns that may also be castellated for the same purpose. A method of using the aperture and grating pattern castellated holographic optical element is also provided.

Having thus described our invention, what we claim as new, and desire to secure by Letters Patent is: 
     
       1. An optical positioning system, for moving a first element having location indicia on a surface thereof, with respect to a second element, which system comprises: a) a coherent light source for illuminating an optical path in the system;   b) a plurality of light detectors positioned to receive light reflected from the first element;   c) a lens array positioned to receive light from said coherent light source and to direct light to predetermined ones of the indicia on the surface of the first element;   d) a servo system responsive to information produced by the first element location indicia for positioning the first and second elements relative to each other in accordance with signals derived from the first element location indicia; and   e) a holographic optical element, positioned in the optical path to direct light to predetermined ones of the first element location indicia, having a plurality of apertures therein with castellations formed on predetermined one or more of aperture edges to create a light energy null at an intended target location.   
     
     
       2. The system according to claim 1 wherein the width and height of holographic optical element's aperture edge castellations are determined as a function of the location at which a light energy null is intended.